Wire ropes are commonly used in a variety of mechanical applications where both strength and flexibility are simultaneously desired such as hoists, elevators, tire cords and the like. Wire rope is generally composed of a plurality (usually six to eight) of preformed strands which are helically wound about a core of hemp, polypropylene or steel wire. The core acts as an elastic support for the strands and is intended to prevent excessive contact stresses between the wires. The individual strands of a rope typically consist of a plurality of wires helically wrapped around a center wire. Until recently little attention has been directed to reducing contact stresses between the individual wires of a strand. In particular, it has only been relatively recently that investigators have begun analyzing the effects of modified strand designs which reduce internal contact stresses between individual wires of a strand.
Prior modifications of the strand geometry were primarily directed to methods wherein wires of circular cross section and/or strands consisting of a plurality of wires are plastically deformed by passing them through a die in order to produce a more solid and compact rope. U.S. Pat. Nos. 251,141; 2,156,652; 3,083,817; 3,778,993; 4,311,001; 4,454,708 and 4,530,205 all generally relate to wire ropes and methods of making wire ropes wherein the wires and/or the wound strands are subjected to compression with the aid of reducing means so as to cause plastic deformation thereof, and to improvements relating to methods which ensure uniform deformation over the cross-section of the strand and/or reduction of the voids therein. This plastic deformation, prevalent in the cited prior art, causes the stranded wires, and ropes, cables and the like made therefrom, to become comparatively stiff and resistant to bending, resulting in a composite structure with properties approaching those of a solid rod-shaped member, thus tending to defeat one of the primary objectives of stranded wire structures which is to provide high load bearing strength in a structure having high bending flexibility.
More recently, Conway, T. A. and Costello, G. A. (1991), Response of a Strand with Elliptical Outer Wires, Int. J. Solids Structures, 28(1), 33-42 disclose a theoretical comparative stress analysis between typical wire ropes having outer wires with a circular cross-section and wires having an elliptical cross-section. The analysis suggests that elliptical outer wires will reduce internal contact stresses by as much as about 25 percent compared with outer wires having a circular cross-section.